The invention relates to microwave frequency filters, particularly those usable in miniaturized light-weight airborne step tuned mixers.
A common receiver component is the down-converter, which mixes the received radio frequency RF signal and a local oscillator LO signal to provide an intermediate IF signal output. A filter is often required in such mixers, to prevent harmful interaction between the LO and IF circuits.
When the receiver must cover a wide bandwidth, it is often helpful to change the LO frequency in discrete steps. If the spacing between the LO steps is small and a large guardband exists between the LO and IF bands, conventional filtering techniques are adequate, G. L. Matthaei, L. Young and E. M. T. Jones, "Microwave Filters, Impedance-Matching Networks and Coupling Structures," McGraw-Hill, 1964, pp. 83-104, 440-450 and 584-595. However, if the LO bandwidth is large and the spacing between the LO and IF bands is narrow, conventional filters require many sections, and the filter can become large and heavy. For airborne receivers, where size and weight must be minimized, conventional multi-section filters are undesirable.
The present invention addresses and solves the need for size and weight reduction in airborne step tuned wideband applications, though the invention is of course not limited thereto.